1. Field of the Invention
The present invention relates to radio-frequency (RF) test equipment for portable radiotelephones. More particularly, the present invention relates to a novel and improved adapter for interfacing a portable radiotelephone with RF test equipment.
II. Description of the Related Art
In the field of cellular communications, portable radiotelephones are used to communicate with base stations over radio-frequencies (RF). As these portable radiotelephones are manufactured, they are typically tested at various stages of production. For example, the individual circuit card assemblies of the radiotelephone are typically tested for functionality and component integrity individually at the "card-level," and in combination at the "subassembly-level," as the portable radiotelephone is assembled. This production typically occurs in a factory setting, where much of the testing is automated, and the circuit cards which will eventually be enclosed in the radiotelephone housing may be substantially exposed. With the radiotelephone circuit cards substantially exposed, access to various test points on the circuit cards is conveniently accommodated. However, once the portable radiotelephone is fully assembled, the circuit cards and other components are typically fully enclosed in the radiotelephone housing, preventing convenient access to the internal portions of the radiotelephone.
It is often desirable to test the RF performance of the radiotelephone under controlled conditions after it is fully assembled, both alone and in conjunction with an associated base station. Additionally, it is often desirable to test the performance of the associated base station itself by interfacing the RF signal of one or more portable radiotelephones directly to the base station. Typically, once the radiotelephone is fully assembled the only access to the RF signal generated by the radiotelephone is at the antenna port. However, there is typically no RF return path available at the antenna port itself because the antenna is normally a simple dipole. Without convenient access to the internal portions of the radiotelephone, it becomes very difficult to interface the radiotelephone to any desired RF test equipment without "jury-rigging" awkward and cumbersome test setups. For example, one solution to the problem would be to create a "virtual ground" by using a large piece of double-sided circuit board to serve as an RF return path. In such a setup, the antenna port could be connected to the top side of the circuit board, with the bottom side serving as the virtual ground. However, such a test setup is impractical due to its large and awkward size, its inability to be calibrated for predictability in testing, high RF signal leakage, and unacceptable RF signal attenuation across the circuit board.
What is needed is an assembly for interfacing a fully-assembled portable radiotelephone with RF test equipment which is small in size, rugged in construction, and easy to use. Such an RF test equipment interface assembly must provide an RF return path which exhibits low RF signal attenuation, i.e. insertion loss, as well as low radiated emission levels.